Histologic grade, DNA ploidy, and percentage tumor area were assessed in prostatectomy specimens from 73 patients with clinical stage B adenocarcinoma of the prostate and analyzed for their value as predictors of tumor progression. Further, the relationship between percentage tumor area and DNA ploidy was studied. Percentage tumor area was the indicator most strongly associated with the likelihood of tumor extension beyond the capsule of the prostate and of tumor progression as assessed in a logistic regression model. Grade was slightly superior to percentage area in predicting time to progression in a Cox model analysis. Increasing percentage tumor area was associated with an increased likelihood of aneuploidy. Little additional predictive ability was obtained with the concurrent use of two indicators in multivariate analysis, suggesting a high degree of interrelatedness of percentage tumor area, histologic grade, and DNA ploidy. DNA ploidy was not an independent predictive factor, and from a practical standpoint histologic grade and percentage tumor area were more important predictors of tumor progression than DNA ploidy.